Multi-destination burst protocol

ABSTRACT

Multicast transmissions are efficient but do not allow for individual acknowledgement that the data was received by each receiver. This is not acceptable for isochronous systems that require specific levels of QoS for each device. A multimedia communications protocol is provided that uses a novel multi-destination burst transmission protocol in multimedia isochronous systems. The transmitter establishes a bi-directional burst mode for multicasting data to multiple devices and receiving Reverse Start of Frame (RSOF) delimiters from each multicast-destination receiver in response to multiple SOF delimiters, thus providing protocol-efficient multi-destination acknowledgements.

PRIORITY CLAIM

This application claimed priority to U.S. Provisional Application forPatent No. 62/094,267 filed Dec. 19, 2014, the disclosure of which isincorporated by reference.

TECHNICAL FIELD

The present invention relates generally to a method and apparatus for apacket-based multi-destination communication protocol which reducespacket latency and jitter in multimedia applications.

BACKGROUND

Communication of multimedia data requires optimum performance in severalparameters in order to provide the data fast enough to preserve thequality of the multimedia services (quality of service—QoS) beingoffered, such as VoIP, audio distribution or video distribution. Thedata rate, i.e., the rate of signaling each data bit or symbol, has tobe fast enough to provide data at the rate of or faster than the rate ofconsumption by the receiving device's application. In packet datacommunications protocols, the data rate is further complicated by thedelay between sending the packets of data. The delay in delivering anindividual packet of data is the packet latency. The variation of thedelay across multiple receive packets is called jitter. In highlycongested shared networks, devices use various methods to contend foraccess to the network so their packets can be sent with low enoughlatency and jitter in order to ensure the necessary QoS requirements ofthe data-consuming application.

In some communications protocols, for example HomePlug® AV and AV2,which are hereby incorporated by reference, a “regular” media accesscontrol (MAC) protocol data unit (MPDU) can be transmitted to areceiving node's physical layer (PHY) of the OSI model and receive anacknowledgement (ACK) back for each successfully transmitted MPDU. Theseprotocols also support a burst mode which allows the transmitter totransmit multiple long MPDUs without relinquishing the medium, andbefore soliciting a response. The response, a selective acknowledgement(SACK) from the receiver back to the transmitter, provides the receptionstatus for all of the MPDU's being sent by the transmitting PHY to thereceiver's PHY. Long MPDUs in burst mode are separated by burstinterfame spacing (BIFS). Because MPDU bursts only require the singleSACK response, the time to send packets and get ACK responses is reducedand the protocol efficiency increases for that communications exchange.In the burst mode, the start of frame (SOF) delimiter contains a counterfield (MPDUCnt) that indicates how many MPDUs follow the current MPDU(with the value “0” indicating the last MPDU in the sequence. FIG. 1shows an example of MPDU bursting as known to those skilled in the art.

The protocols cited above also also allow for bidirectional bursting. Inthis mode, transmitter allows part of the time it reserved to burst datato the receiver for the receiver to send data back to the originaltransmitter. It serves as an effective back channel that does not needto be negotiated with the network. The receiving station initiatesbi-directional bursting by sending “request reverse transmission flag”(RRTF) and “request reverse transmission length” (RRTL) fields in theframe control section of the SACK. The RRTL field specifies the minimumrequired frame length for the Reverse SOF (RSOF) MPDU. Upon receivingthe request, the original transmitter decides whether to honor therequest and the duration. Obviously, if the request is for more timethan the original transmitter has reserved, it will be denied.

FIG. 2 illustrates an example of the bidirectional burst mechanism asknown in the art. When the receiver (Dev B) determines that it wants totransmit in the reverse direction, it sets the RRTF and RRTL fields inthe SACK or RSOF. This is set until the original transmitter (Dev A)responds, granting the request for the maximum duration, or until thereis no longer a need to request a transmission in the reverse direction.

FIG. 3 shows the various interframe spaces during a bidirectional burst.These spaces result in increased latency (reduced efficiency).

The burst mode does not support communicating with more than one deviceduring a burst which means that each individual communication with areceiver has to be initiated separately. A better method is needed toimprove packet latency and hence communications efficiency in congestedmultimedia networks.

SUMMARY OF THE INVENTION

In an embodiment, a multimedia communications protocol is presented thatsolves the problem of excessive packet latency and jitter by enablingcommunications between a transmitter and individual receivers (i.e.,“multi-destinations”) by using multicast distribution (one to many) andestablishing separately the pseudo contention free periods (PCFP) withina bidirectional burst mode for acknowledgments from the individualreceivers. A Start of Frame delimiter for each receiver in the multicastdistribution group establishes the specific PCFP within in which eachreceiver sends an acknowledgement. The disclosed protocol and method hasthe ability to be used within existing CSMA-based protocols whilemaintaining compatibility.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates an example of a MPDU bursting sequence;

FIG. 2 illustrates an example of the bidirectional burst sequence:

FIG. 3 illustrates interframe spacing used in bidirectional bursting;

FIG. 4 illustrates the pseudo contention free period according to anembodiment; and

FIG. 5 illustrates an example of a CSMA protocol using themulti-destination SOF and RSOF protocol according to an embodiment.

DETAILED DESCRIPTION OF THE DRAWINGS

The making and using of embodiments are discussed in detail below. Itshould be appreciated, however, that the present disclosure providesmany applicable inventive concepts that may be embodied in a widevariety of specific contexts. The specific embodiments discussed aremerely illustrative of specific ways to make and use the invention, anddo not limit the scope of the invention.

Embodiments herein are described, without limitation, in a specificcontext of a protocol method and apparatus used to minimizecommunications packet latency and jitter for data used by multimediadevices such as audio systems wherein all of the individual networkdevices act as a group that has isochronous QoS requirements in order todeliver one combined experience. This disclosure also uses the HomePlugAV specification as contextual framework (including terms) forpresenting the invention, although the disclosed invention is notlimited to that protocol. The HomePlug AV specification specificallydefines a bidirectional bursting protocol that uses SOFs and RSOFs forsequential MPDU payload transmissions and acknowledgements, however thisprocess is only specified from one transmitter to one receiver. It isspecifically not applicable to multicast transmissions with multipledestinations and consequently is not as efficient for reducing packetlatency as the disclosed method. In this disclosure, “receiver” is atopology term to help distinguish between a multicast transmitter andthe receiving multicast destinations, but all transmitters and receiversdescribed here are functionally transceivers.

In accordance with the present disclosure, network initialization datais programmed, by one or more methods such as a user interface or at thetime of manufacture or a discovery protocol, with the data about deviceson the network that are part of a group of multimedia devices on thenetwork that function together, such as an audio sound system that isrendering one music file. The digital information includes identifiers(such as device ID, MAC ID, Link ID), topology digital information (suchas a sequence number for all of the devices in the network that definethe device order within the group), a sequence back-off value, as wellas delimiter frame lengths and other information as embodied below. Theinitialization data can be field programmable in order to allowequipment to be replaced or repurposed after the sale or installation.

In accordance with an embodiment, FIGS. 4 and 5 illustrate amulti-destination protocol method using multiple pseudo contention freeperiods comprising multiple SOFs. Each SOF and associated pseudocontention free period is used for one of the multicast receiver'sacknowledgment. When a transmitter 500 has won a CSMA contention process400 of a carrier sense multiple access (CSMA) protocol, the transmittertransmits a start of frame (SOF) delimiter 410 which contains dataincluding the frame length (FL) field 420 (a digital value representingduration in time). The SOF keeps the channel reserved for thetransmitter to communicate with the multicast group. It also transmitsthe MAC protocol data unit (MPDU) payload 430. The multicasttransmission is addressed to all “n” members of a group of receivingdevices 520, 530 that share a common function such as the audio speakersystem previously mentioned. The SOF and MPDU are followed by a pseudocontention free acknowledgment period (PCFP) 440 that last for the FrameLength (FL) duration 425 a minus the time the MPDU payload 430 uses.During the pseudo contention free acknowledgment period 440 a, one ofthe devices in the group acknowledges the status of the multicast packetusing a reverse start of frame (RSOF) delimiter 590 a. The delimiter canbe sent as soon as a RSOF interframe space allows the transmitter andreceiver to switch roles. Which receiver responds is determined inadvance of this protocol using a Link ID or a group sequence number sothat only one device responds per SOF. As soon as the RSOF 590 a isreceived, or just before the FL duration 425 a expires, a subsequentSOF_(n) 540 is transmitted to continue the PCFP for a new duration 425b. The SOF₂ also contains the identity of a member of the multicastgroup that may respond with a RSOF₂ 590 b during the new PCFP 440 b.Subsequent SOFs are transmitted until all of the devices in the grouphave had the opportunity to acknowledge the multicast packet. Theconcatenated PCFPs ends when the last device transmits a SACK 430delimiter, the last FL duration expires, or the maximum concatenatedPCFP durations allowed by convention has been reached (typically 5 to 10ms). Any group device can terminate the multi-destination protocol earlyby sending a SACK during the PCFP. If a receiver fails to acknowledgethe SOF, the original transmitter can send another SOF directed to thereceiver.

In one embodiment, the SOF 410 can be retransmitted before thesubsequent SOFs 540 if the RSOF 590 a has not been received within thePCFP 440 a.

In another embodiment, the acknowledgment contains digital informationabout the quality of the received data and the communications channel.The tone map associated with each SOF may be different so thatcommunications with specific receivers may be optimized for the bestpossible combination of tone map parameters (such as convolution codingrate, bit loading, tone map, etc.) in order to optimize thecommunications efficiency. The transmitter may also analyze the qualitydata provided by all of the acknowledgements from the multicast groupand decide on an improved tone map for the entire group of receivers.

By modifying the SOF delimiter to specifically request acknowledgmentsfrom receivers that were addressed in the multicast, separatetransactions to send the same MPDU payload to multiple destinations andthe interface spacings are avoided and the latency and jitter betweenmulticast MPDUs is reduced.

The disclosed protocol method is an independent method but is alsocompatible with and can be used to modify existing native protocols suchas the IEEE 802.11 series standard, the IEEE 1901-2010 standard andHomePlug AV-based specifications. The ability to hold off a transmissionfor an acknowledgement period is similar to HomePlug AV's bidirectionalburst method except that the protocol herein modifies the SOF and RSOFdelimiters to support multi-acknowledgements from multiple receiverswhich is specifically not permitted or anticipated in HomePlug AV. Bymodifying an existing mechanism, the protocol herein can be initializedusing compatible delimiters and operates within the acknowledgementperiod which is isolated from and can contain a protocol that isdifferent from the native protocol, without affecting the nativeprotocol. In this way the protocol can be used to modify an existing(native) protocol to support the protocol herein.

In addition, if the transmitter determines that due to thecommunications quality, the communications improvement provided by thisprotocol is less than that which can be accomplished by native methods,the multi-destination protocol may be switched off until channelconditions improve, without affecting the compatibility andinteroperability with the native protocol.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare considered illustrative or exemplary and not restrictive; theinvention is not limited to the disclosed embodiments. Other variationsto the disclosed embodiments can be understood and effected by thoseskilled in the art in practicing the claimed invention, from a study ofthe drawings, the disclosure, and the appended claims.

What is claimed is:
 1. A method for multicast communications in acarrier sense multiple access (CSMA) network including a transmitter anda multicast group of receiving devices including at least two receivingdevices, the method comprising: making a multicast transmission to themulticast group using a Start of Frame (SOF) delimiter that includes aframe length of a first bidirectional burst pseudo contention freeperiod during which the transmitter communicates without contention;wherein the SOF further includes an identification of a first one of thereceiving devices in the multicast group that is allowed to transmit ina first pseudo contention free period; responding by said first one ofsaid receiving devices to the first SOF delimiter with a firstacknowledgement of status of received multicast media access control(MAC) protocol data unit (MPDU) data; transmitting a second SOF beforean end of the frame length of the first SOF that is addressed to asecond one of the receiving devices; acknowledging by the second one ofthe receiving devices the status of the received multicast MPDU datausing a second acknowledgement; and continuing subsequent SOF andacknowledgement process until one of: a last one of the receivingdevices in the multicast group has been addressed by a SOF and hasresponded or the first bidirectional burst is terminated.
 2. The methodof claim 1, wherein the acknowledgement is a Reverse SOF (RSOF)delimiter.
 3. The method of claim 1, wherein the last receiver in thegroup responds with a selective acknowledgement (SACK) in order toterminate the first bidirectional burst.
 4. The method of claim 1,wherein any receiver in the multi-destination protocol sequence canterminate the first bidirectional burst by sending a selectiveacknowledgement (SACK).
 5. The method of claim 1, wherein theacknowledgement contains digital information about communicationsquality, and further comprising using said digital information aboutcommunications quality by the transmitter to determine best parametersto use in a common Tone Map for subsequent multicast transmissions. 6.The method of claim 1, wherein the acknowledgement contains digitalinformation about communications quality, and further comprising usingsaid digital information about communications quality by the transmitterto determine best parameters to use for all SOFs in order to optimizeacknowledgement transmissions from the receivers.
 7. The methods ofclaim 1, wherein a link identification (LID) is used by different SOFsto identify the multicast group member which is allowed to acknowledgethe multicast MPDU data.
 8. The method of claim 1, wherein theacknowledgement contains digital information about communicationsquality, and further comprising using said digital information aboutcommunications quality by the transmitter to determine best parametersto use for each SOF for that device in order to optimize acknowledgementtransmissions from the receivers.
 9. A method for use in acommunications system including a carrier sense multiple access (CSMA)network including a transmitter and a multicast group of receivingdevices including at least two receiving devices, the method comprising:making a multicast transmission to the multicast group using a Start ofFrame (SOF) delimiter addressed to a first one of the receiving devicesthat determines a frame length of a first bidirectional burst pseudocontention free period during which the transmitter communicates withoutcontention; wherein the SOF comprises an identification of the first oneof the receiving devices in the multicast group that is allowed totransmit in the first pseudo contention free period; responding by thefirst one of the receiving devices to the first SOF delimiter with afirst acknowledgement to indicate the status of received multicast mediaaccess control (MAC) protocol data unit (MPDU) data; transmitting asecond SOF before the end of the frame length of the first SOF that thatis addressed to a second one of the receiving devices, acknowledging bythe second one of the receiving devices the status of the receivedmulticast MPDU data using a second acknowledgement; continuingsubsequent SOF and acknowledgement until one of: a last one of thereceiving devices in the multicast group has been addressed by a SOF andresponded, or the first bidirectional burst is terminated; and whereinthe multicast transmission does not adversely affect interoperabilitywith a native CSMA protocol within which the multicast transmission isused.
 10. The method of claim 9, wherein the acknowledgement is aReverse SOF (RSOF) delimiter.
 11. The method of claim 9, wherein thelast receiver in the group responds with a selective acknowledgement(SACK) in order to terminate the first bidirectional burst.
 12. Themethod of claim 9, wherein any receiver in the sequence can terminatethe first bidirectional burst by sending a selective acknowledgement(SACK).
 13. The method of claim 9, wherein the acknowledgement containsdigital information about communications quality, and further comprisingusing the digital information about communications quality by thetransmitter to determine best parameters to use in a common Tone Map forsubsequent multicast transmissions.
 14. The method of claim 9, whereinthe acknowledgement contains digital information about communicationsquality, and further comprising using the digital information aboutcommunications quality by the transmitter to determine best parametersto use for all SOFs in order to optimize acknowledgement transmissions.15. The method of claim 9, wherein a link identification (LID) is usedby different SOFs to identify the group member which is allowed toacknowledge the multicast MPDU data.
 16. The method of claim 9, whereinthe acknowledgement contains digital information about communicationsquality, and further comprising using the digital information aboutcommunications quality by the transmitter to determine best parametersto use for each SOFs in order to optimize acknowledgement transmissions.